Hi, please try this : uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files , C:\Program Files(x86) & C:\ProgramData Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 59.0.2 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

Note fyi : check to see if have Microsoft update KB4093105 700megs If not you can get it here : https://www.catalog.update.microsoft.com/Search.aspx?q=kb4093105 Note fyi : Windows Spring Update out April 30th so back up stuff you want to save to another drive. https://www.windowscentral.com/microsoft-announces-windows-10-april-2018-update

Thank you, PkShadow. I still can't see the preview; however, I do have a theme that shows up and using it. I can still only see the name and image of the theme. If I go into "customize", I then can see any theme I downloaded and choose from there. I have done something wrong either the order or I didn't delete all of the items you suggested. I think I'll just use it as is right now and maybe later try following your instructions a little closer. Thank you much.

Hi, welcome. Not may want to do it sooner as Firefox ver 59.0.3 released today to be compatible with Windows 10 Spring Update Released today : https://www.windowscentral.com/how-get-windows-10-april-2018-update Update all your programs 1st then download the Media Creation Tool and choose upgrade if you are going to do so.